1. Technical Field
The present invention generally relates to a combustion chamber for internal combustion chamber engines that are fueled by atomized fuel directly supplied into the combustion chamber, and deals more particularly with combustion chambers in which air flow is created and the atomized fuel is mixed with the air flow whereby to achieve an improvement in the air utilization rate, a decrease of exhaust unburnt particulate matter, and a decrease in the smoke index or density, as well as to obtain a desired power output.
2. Background Art
For a combustion chamber of internal combustion engines of the type that has its fuel atomized and directly fed into the combustion chamber which is formed as a compartment within the piston, such as the diesel engines, the troidal type of combustion chamber shown in FIG. 8 is typical.
As shown in FIG. 8, in the troidal combustion chamber b that is formed by a recess in the top part of piston a, there is disposed a fuel injection nozzle c, having generally four nozzle holes d, aligned in a circle facing the combustion chamber b. This arrangement is disclosed in Japanese Utility Model Laid Open No. 193,013/1983. Here, each nozzle hole d of the fuel injection nozzle c is designed so as to make the length of flight of its fuel mist e approximately the same, so that good fuel distribution will result.
However, investigation of the preformance of such a combustion chamber described above in terms of the smoke index (in bosch number) with regard to the engine revolution speed has revealed an observation illustrated in FIG. 9. Specifically, as shown in FIG. 8 by the double-dot line I, the smoke index of a fuel injection nozzle having four jet nozzles is high, i.e. its smoke performance is unfavorable. This is because mixing of the atomized fuel and air in the combustion chamber is unsatisfactory.
As the next step in the investigation, one more jet nozzle was added, and the five nozzle holes were distributed so as to face the periphery of the combustion chamber. The result, which is represented by the broken line II, was that, even though the smoke index was lower for lower engine revolution speeds, it became higher than the case of four nozzles beyond a certain revolution speed.
This is because an increase in the number of the nozzle holes decreases the peripheral intervals between them, and although this arrangement does bring about improved dispersion of fuel mist while the engine revolution speed is low, the swirl generated becomes more apt to carry the fuel sprays over and toward the center of the combustion chamber as the revolution speed is raised, thereby destroying the favorable distribution of the fuel mist.
That is to say, such a state of conditions as mentioned above is equivalent to having an overswirl in the combustion chamber, and since overswirling tends to concentrate the fuel-air mixture in the center axis portion thereof, decreasing the air utilization rate and causing generation of HC and smoke, it is unfavorable for combustion.